Investigation of 2-[(<Emphasis Type="Italic">E</Emphasis>)-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3H-indolium as a new highly sensitive reagent for the spectrophotometric determination of nitrophenols

A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of nitrophenols [picric acid (PA); dinitrophenols (DNP)] in wastewater samples. The method is based on the reaction of nitrophenols with 2-[(E)-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3 H-indolium chloride reagent to form the colored ion associates, which are extracted by organic solvents. The molar absorptivity of the ion associates of PA with the investigated reagent ranges from 8.3×10⁴ to 11.3×10⁴ L mol^–1 cm^–1, depending on the extractant. Because only PA is extracted in an acidic medium with the investigated reagent, but both PA and DNP are extracted in an alkaline medium, it is possible to determine both substances in a mixture. Appropriate reaction conditions have been established. The absorbance of the colored extracts obeys Beers law in the range of 0.04–4.58 mg L^–1 PA, 1.0–18.4 mg L^–1 2,4-DNP and 1.2–14.7 mg L^–1 2,6-DNP, respectively. The limit of detections, calculated from a blank test (n=10; P=0.95), are 0.05 mg L^–1 PA, 0.9 mg L^–1 (2,4-DNP), and 1.1 mg L^–1 (2,6-DNP), respectively.     

The composition analysis of YBa2Cu3O7-δ or PrBa2Cu3O7-δ thin films and (YBa2Cu3O7-δ/PrBa2Cu3O7-δ)n heterostructures prepared by CVD

Some YBa₂Cu₃O_7-δ films and heterostructures prepared by Chemical Vapor Deposition (CVD) were analyzed in our laboratories by EPMA-EDX or WDX, RBS, SNMS and AES. It was found that in some cases the results of composition analysis can significantly deviate from each other. At least two main reasons for these deviations exist: the different lateral resolution and the application of different reference samples for the calibration. Received: 3 June 1996 / Revised: 14 October 1996 / Accepted: 16 October 1996     

MO-LCAO Calculations of Polymethines

Idealized polymethines are defined as conjugated chain molecules with complete bond equilization and charge alternation. A constant π-bond order along the chain with N atoms has been derived for three types of polymethines which differ by the nature of the heteroatomic end groups. Corresponding to the number of π-electrons they are termined (N + 1)π-, Nπ- or (N ? 1)π-polymethines. This classification embraces closed shell as well as open shell systems. The relations for the energy eigenvalues, coefficients and derived quantities have been obtained in closed form. The results for the different classes of polymethines are strongly related. Their molecular properties should be similar.     

Accurate pKa determination for a heterogeneous group of organic molecules.

Single-molecule studies that allow to compute pKa values, proton affinities (gas-phase acidity/basicity) and the electrostatic energy of solvation have been performed for a heterogeneous set of 26 organic compounds. Quantum mechanical density functional theory (DFT) using the Becke-half&half and B3LYP functionals on optimized molecular geometries have been carried out to investigate the energetics of gas-phase protonation. The electrostatic contribution to the solvation energies of protonated and deprotonated compounds were calculated by solving the Poisson equation using atomic charges generated by fitting the electrostatic potential derived from the molecular wave functions in vacuum. The combination of gas-phase and electrostatic solvation energies by means of the thermodynamic cycle enabled us to compute pKa values for the 26 compounds, which cover six distinct chemical groups (carboxylic acids, benzoic acids, phenols, imides, pyridines and imidazoles). The computational procedure for determining pKa values is accurate and transferable with a root-mean-square deviation of 0.53 and 0.57 pKa units and a maximum error of 1.0 pKa and 1.3 pKa units for Becke-half&half and B3LYP DFT functionals, respectively.     

The synthesis of 1-alkyl-4a-(4-chlorophenyl)- 4,4a-dihydropyrimido[6,1-a]isoindol-9(3H)-one

The primary amino group of 3-(2-aminoethyl)-3-(4-chlorophenyl)-2,3-dihydro-1H-isoindol-1-one ( 1 ) was acylated with acetyl chloride, benzoyl chloride and phenyl acetyl chloride to form the amides 2a -c, respectively. These were cyclized in phosphorus oxychloride to give the 1-substituted-4a-(4-chlorophenyl)-4,4a-dihydropyrimido [6,1-a]isoindol-9(3H)-ones 3a-c . Heating of 1 in formic acid lead to the formation of 4a-(4-chlorophenyl)-4,4a-dihydropyrimido[6,1-a]isoindol-9(3H) -one (3d) . Heating of 1 in the presence of phosgene lead to the formation of 4a-(4-chlorophenyl)-2,3,4,4a-tetrahydropyrimido[6,1-a]isoindole-1, 9-dione (4).     

Mecanismes de Fragmentation de l'Oxazole

The fragmentation mechanisms of oxazole have been studied in detail on using various experimental techniques (refocusing of metastable ions, deuteration, AP measurements) and by theoretical calculations.